An article from WordPress – “ Combating Comment Spam ”

Akismet

Akismet is a comment spam filter from the same people who develop WordPress. After activating it from your Dashboard (“Plugins”, find Akismet, then click “Activate”) you have to perform some additional steps to configure it. 

1. Navigate to “Settings”, then “Akismet”.
2. Click the “Get your API key” button. You will be sent to the Akismet site to get a code for the plugin.
3. On the Akismet site, click the “Activate Akismet” button.
4. You will be asked to log in to a WordPress.com account. This is a different account than your Publish @ Illinois account. If you already have a blog on WordPress.com then you can log in with that account username and password. Otherwise you will have to sign up for a new account. Make sure your password is unique to WordPress.com. It is dangerous to reuse passwords on the internet.
5. Once you have created or logged in with your WordPress.com account you will be shown a page with Akismet plans.
6. The plan option to choose “Personal”. Under the text “Name your price” click the “Get Personal” button.
7. On the payment page, in the right hand column, it asks “What is Akismet worth to you?” If you would like to donate to the Akismet project you can use the slider to chose an amount. Otherwise, move the slider entirely to the left until it reads “$0.00/yr”. This will remove the payment options and only request a first and last name from you. After filling out the name, site URL, and verification fields click the “Continue” button.
8. It will tell you that you are adding a site. Click the "Activate this site" link.
9. You should now have an Akismet API key! Akismet can add it to your WordPress site automatically, just click "Save changes" if it does. If automatically adding it fails, copy the API key and paste it into the box on step (2) labeled “Manually enter an API key”. Click the “Use this key” button.
10. If everything went correctly you should be presented with a page that says “ Akismet is now protecting your site from spam.”

Once you have completed these steps, the interface option to allow public commenting will be enabled. To enable public comments, visit your Dashboard, then choose Settings->Discussion and uncheck the box next to "Users must be registered and logged in to comment (Signup has been disabled. Only members of this site can comment.)"

Some Other Helpful Plugins:

Delete Pending Comments – This plugin is a fast way to delete ALL pending comments. Be sure you wish to delete them all before proceeding. This plugin is great for when there is a large amount of spam in your comments that you don’t want to manually clean up.

Delete All Comments – If your site is overwhelmed with spam comments and you would like to start fresh, the Publish @ Illinois administrators can delete all the comments on your site (pending and approved). Please email consult@illinois.edu if you would like all your comments removed.